Nickel-silicon compound forming method, semiconductor device manufacturing method, and semiconductor device

ABSTRACT

A nickel-silicon compound forming method is disclosed which comprises forming nickel on at least one of only silicon and a compound containing silicon, and performing stepwise-heating of the nickel together with the at least one of only silicon and the compound containing silicon.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/405,999, filed Mar. 31, 2003, now abandoned which is based upon andclaims the benefit of priority from the prior Japanese PatentApplication No. 2002-268863, filed Sept. 13, 2002, the entire contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique capable of improving theelectrical characteristics of a semiconductor device and, in particular,to a nickel-silicon compound forming method, semiconductor devicemanufacturing method, and semiconductor device which can improve theelectrical properties of a transistor.

2. Description of the Related Art

Recently, various types of semiconductor devices represented by an LSIhave been greatly developed owing to micronization and high-integrationof various types of semiconductor elements represented by a transistor.One factor of this may, for example, be a size reduction in a transistorwhich leads to a lower resistance and a larger amount of current flow ona small transistor. However, as the on resistance of the transistordecreases, the parasitic resistances in the source, drain, and gatewhich are the main parts of the transistor become non-negligible. Todecrease the parasitic resistances in, e.g., a source, drain, and gate,a compound called a silicide or salicide that is a compound of a metaland silicon has been started in use. For example, titanium (Ti),tungsten (W), or cobalt (Co) is generally used as a material of asilicide.

However, as the gate of a transistor nowadays has a size of 50 nm orless, nickel (Ni) has received attention as a silicide material withlower resistance. For example, nickel mono silicide (NiSi) has a lowercontact resistance and resistivity than that of a silicide containingTi, W, or Co. Thus, NiSi has been expected as a feature silicide orsalicide material that is to form the main part of a transistor.

In a general semiconductor device manufacturing process, it is ideal toform an NiSi film capable of withstanding high temperatures of 500° C.or more. However, after an Ni film is formed on an Si film, an NiSi filmis typically formed by increasing the temperature to near 350° C. atonce. This is because when the NiSi film is to be formed by increasingthe temperature to near 500° C. at once, cohesion occurs in the NiSifilm, and its composition changes into NiSi₂ to increase theresistivity. To avoid this problem, it has been a common practice toform an NiSi film at a low temperature near 350° C. Consequently,annealing at a high temperature cannot be performed after NiSi filmformation, and this prevents practical use of the film in the varioustypes of semiconductor devices represented by LSIs.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided anickel-silicon compound forming method comprising forming nickel on atleast one of only silicon and a compound containing silicon, andperforming stepwise-heating of the nickel together with the at least oneof only silicon and the compound containing silicon, wherein atemperature is raised and maintained alternately.

According to another aspect of the invention, there is provided asemiconductor device manufacturing method comprising forming anickel-silicon compound on a semi conductor element comprising at leastone of only silicon and a compound containing silicon, wherein thenickel-silicon compound is formed on the semiconductor element byforming nickel on the at least one of only silicon and the compoundcontaining silicon, and performing stepwise-heating of the nickeltogether with the at least one of only silicon and the compoundcontaining silicon, wherein a temperature is raised and maintainedalternately.

According to a further aspect of the invention, there is provided asemiconductor device comprising a semiconductor element, wherein thesemiconductor element has a portion formed by at least one of onlysilicon and a compound containing silicon, a nickel-silicon compound isformed on the portion, and the nickel-silicon compound is formed on theportion by forming nickel on the at least one of only silicon and thecompound containing silicon, and performing stepwise-heating of thenickel together with the at least one of only silicon and the compoundcontaining silicon.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a graph showing a change in temperature in a nickel-siliconcompound forming method according to the first embodiment;

FIG. 2 is a graph showing the temperature dependence of the sheetresistance of an NiSi film formed on an Si substrate by thenickel-silicon compound forming method according to the firstembodiment;

FIG. 3 is a sectional view showing the NiSi film formed on the Sisubstrate by the nickel-silicon compound forming method according to thefirst embodiment;

FIG. 4A is an electron microscope photograph which shows the surfacestate of an NiSi film formed at 800° C. on an Si substrate by thenickel-silicon compound forming method according to the firstembodiment;

FIG. 4B is an electron microscope photograph which shows the surfacestate of an NiSi film formed at 900° C. on an Si substrate by thenickel-silicon compound forming method according to the firstembodiment;

FIG. 5 is an electron microscope photograph which shows SiGe underlyingan NiSi film on an Si substrate according to the second embodiment;

FIG. 6 is a sectional view showing SiGe underlying the NiSi film on theSi substrate according to the second embodiment;

FIG. 7 is a sectional view showing the NiSi film and the structure neara transistor of a semiconductor device according to the secondembodiment; and

FIG. 8 is a graph showing the temperature dependence of the sheetresistance of the NiSi film formed on SiGe according to the secondembodiment.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described below in detail with referenceto the accompanying drawings.

First Embodiment

The first embodiment will be described first with reference to FIGS. 1to 4A and 4B. FIG. 1 is a graph showing a change in temperature in anickel-silicon compound forming method according to this embodiment.FIG. 2 is a graph showing the temperature dependence of the sheetresistance of an NiSi film formed on an Si substrate by thenickel-silicon compound forming method according to this embodiment.FIG. 3 is a sectional view showing the NiSi film formed on the Sisubstrate by the nickel-silicon compound forming method according tothis embodiment. FIGS. 4A and 4B are electron microscope photographswhich show the surface states of NiSi films formed at 800° C. and 900°C., respectively, on Si substrates by the nickel-silicon compoundforming method according to this embodiment.

In this embodiment, a case wherein a nickel mono silicide (NiSi) filmserving as a nickel-silicon compound is formed on a silicon (Si)substrate will be described.

As shown in FIG. 3, first, a nickel (Ni) film 1 is deposited on a p-typesilicon substrate 2. This embodiment uses the Si substrate (siliconwafer) 2 with plane indices (1 0 0). The Si (1 0 0) substrate 2 issimply referred to as the Si substrate 2, hereinafter. The Si substrate2 is cleaned by a hydrofluoric acid (HF) which is diluted in advancebefore deposition of the Ni film 1. The Ni film 1 is deposited on the Sisubstrate 2 by sputtering until the Ni film 1 has a thickness of about30 nm.

The Si substrate 2 with the Ni film 1 is then silicided. Morespecifically, this process has a characteristic feature that the Ni film1 is heated stepwise together with only Si or an Si compound. Suchstepwise heating is particularly referred to as a multi-step annealing.

The Si substrate 2 with the Ni film 1 undergoes the multi-stepannealing. This multi-step annealing is performed by using a rapidthermal anneal system (RTA system: not shown). More specifically, themulti-step annealing of this embodiment is so performed as to make achange in temperature therein along with the graph shown in FIG. 1.

First, the Si substrate 2 with the Ni film 1 is heated to increase theirtemperature from a temperature T₀ to a temperature T₁. Thereafter, theNi film 1 and Si substrate 2 are heated stepwise. That is, a step ofincreasing, by a temperature ΔT over a period of time S₁, thetemperature of the Ni film 1 and Si substrate 2 that has been increasedfrom the temperature T₀ to the temperature T₁ and keeping the resultanttemperature for a period of time S₂ is repeated a plurality of times.These steps heat the Ni film 1 and Si substrate 2 from the temperatureT₀ to the temperature T₂ stepwise.

More specifically, first, the temperature of the Ni film 1 and Sisubstrate 2 is rapidly increased from about 0° C. to about 300° C. atonce. Subsequently, the temperature of the Ni film 1 and Si substrate 2that has been increased at about 300° C. is further increased by about50° C. over 10 sec. That is, the Ni film 1 and Si substrate 2 are heatedfrom the temperature of about 300° C. to about 350° C. in 10 sec.Thereafter, the temperature of the Ni film 1 and Si substrate 2 is keptat about 350° C. for 30 sec. The step of increasing the temperature ofthe Ni film 1 and Si substrate 2 by about 50° C. over 10 sec and keepingthe resultant temperature for 30 sec is then repeated nine times. Withthis processing, the temperature of the Ni film 1 and Si substrate 2 isincreased from about 300° C. to about 800° C. stepwise. That is, the Nifilm 1 and Si substrate 2 are heated and heat-insulated 10 times eachhaving a period of almost 40 sec/step, so that their temperature isincreased from about 300° C. to about 800° C. stepwise. This period isreferred to as a ramp-up period. In this embodiment, the temperature ofthe Ni film 1 and Si substrate 2 is increased from about 300° C. toabout 800° C. over a total of about 400 sec stepwise.

After the Ni film 1 and Si substrate 2 are heated to have thetemperature of about 800° C., their temperature is kept at about 800° C.for a period of time almost equal to that required for the heatingsteps. The Ni film and Si substrate are then cooled and rapidlydecreased in temperature from about 800° C. to about 0° C. at once. Asshown in FIG. 1, the multi-step annealing of this embodiment requiresabout 800 sec per process. A nickel mono silicide film (NiSi film) 3 isformed on the Si (1 0 0) substrate 2 by the above-described steps.

According to experiments that have been conducted by the presentinventors, in the NiSi film 3 formed by the multi-step annealing of thisembodiment, cohesion and a change in its composition into NiSi₂ hardlyoccurred. In addition, as shown in FIG. 2, the sheet resistance of theNiSi film 3 in this embodiment can be kept as low as a maximum of about10 Ω/□ up to about 800° C. This is a good value that can be sufficientlyapplied even to a fine transistor having a gate with a size of about 50nm or less. Further, as shown in FIG. 4A, the surface of the NiSi film 3in this embodiment can be kept in a smooth, good, and almost uniformstate without roughness up to 800° C. That is, the surface of the NiSifilm 3 can be kept in a so-called mirror-surface state or a cleaned goodstate up to 800° C. This is a good state that can be sufficientlyapplied even to a fine transistor having a gate with a size of about 50nm or less. The temperature of about 800° C. is sufficiently higher thanthat for a process such as a general LSI wiring step.

Therefore, the NiSi film 3 in this embodiment has a very highapplicability to various types of semiconductor elements, e.g., a MOStransistor and the like, and to various types of semiconductor devicesincluding various types of semiconductor elements, e.g., an LSI and thelike. That is, the NiSi film 3 in this embodiment has a very highpracticability. However, as shown in FIG. 4B, cohesion and the likeoccur on the surface of the NiSi film 3 at the temperature of about 900°C., so a smooth and almost uniform mirror-surface state cannot beobtained at this temperature. Experiments that have been conducted bythe present inventors reveal that the NiSi film 3 formed by heating itto about 800° C. by the multi-step annealing of this embodiment canmaintain good quality up to 800° C. even in annealing that is performedthereafter. That is, the NiSi film 3 formed by the multi-step annealingof this embodiment can maintain good quality in subsequent annealing upto a maximum temperature to which the film has been exposed in filmformation.

Inspections that have been conducted by the present inventors by usingan X-ray diffraction (XRD) method reveal that almost all nickel silicide(NiSi_(x)) films 3 can be formed as the nickel mono-silicide (NiSi)films 3 by setting a proper film formation environment. In addition, thestoichiometric ratio of the NiSi film 3 formed by the multi-stepannealing of this embodiment greatly depends on the temperature increaserate and temperature keeping time in the stepwise heating step. That is,according to the multi-step annealing of this embodiment, when atemperature increase rate and temperature keeping time are appropriatelyregulated to proper values, NiSi_(x) films 3 of desired qualityincluding an NiSi film 3 can be formed.

As described above, according to the first embodiment, an NiSi film 3 ofgood quality which can be improved in electrical characteristics and hasa stable composition even at high temperatures of about 500° C. or morein a general semiconductor device manufacturing process can be formed onthe Si substrate 2. Accordingly, NiSi films 3 with very highpracticability can be formed as materials of forming various types ofnext-generation semiconductor elements represented by, e.g., a finetransistor having a gate with a size of about 50 nm or less. An NiSifilm 3 with very high practicability that is well suited tonext-generation semiconductor devices represented by a very finehigher-integrated LSI with higher-performance which includes finesemiconductor elements can be formed.

Second Embodiment

The second embodiment will be described next with reference to FIGS. 5to 8. FIG. 5 is an electron microscope photograph which shows SiGeunderlying an NiSi film on an Si substrate according to this embodiment.FIG. 6 is a sectional view showing SiGe underlying the NiSi film on theSi substrate according to this embodiment. FIG. 7 is a sectional viewshowing the NiSi film and the structure near a transistor of asemiconductor device according to this embodiment. FIG. 8 is a graphshowing the temperature dependence of the sheet resistance of the NiSifilm formed on SiGe according to this embodiment. A detailed descriptionof the same parts as in the first embodiment is omitted.

In this embodiment, a case wherein an NiSi film is formed on the silicongermanium (SiGe) film which, in turn, is formed on an Si substrate willbe described. More specifically, NiSi films are formed on the source anddrain of a transistor that are elevated on the surface of the Sisubstrate by using a compound containing Si (SiGe). A nickel-siliconcompound forming method, semiconductor device manufacturing method, andsemiconductor device according to this embodiment will be describedtogether along the order of steps in the semiconductor devicemanufacturing method.

As shown in FIGS. 5 and 6, first, a silicon germanium (SiGe) film 12 isformed on an Si substrate 11. As the Si substrate 11, the same Si (1 00) substrate 11 as in the first embodiment is used. On the surface ofthe Si substrate 11, an insulating film layer (insulating isolationregion pattern) 13 made of a predetermined pattern is oxidized andformed in advance. The SiGe film 12 is selectively formed on the Sisubstrate 11 by epitaxial growth. This will be described in detailbelow.

More specifically, the SiGe film 12 is deposited on the Si substrate 11by UHV-CVD which uses Si₂H₆ and GeH₄ as gas sources. This UHV-CVD isperformed by using an UHV-CVD system (not shown). The ultimate pressureof the UHV-CVD system is 10⁻¹⁰ Torr. The pressure during epitaxialgrowth is 10⁻⁵ Torr or less. The growth chamber of the UHV-CVD system iscooled by liquid nitrogen during epitaxial growth. The SiGe film 12 isthermally cleaned at about 800° C. and then epitaxially grown at about630° C. The composition of germanium (Ge) on the SiGe film 12 iscontrolled by changing the flow rate of the gas sources Si₂H₆ and GeH₄.

FIG. 5 shows an electron microscope image of the section of the SiGefilm (SiGe layer) 12 which has been selectively formed on the Sisubstrate 11 by epitaxial growth. The epitaxially-grown SiGe film 12 hada thickness of about 60 nm. In addition, no SiGe film 12 was formed onthe uppermost portion of the TEOS film 13 serving as the insulating filmlayer (insulating isolation region pattern). That is, no SiGe film 12was epitaxially grown on the TEOS film 13.

As shown in FIG. 7, an NiSi film 14 is formed on the SiGe film 12. TheNiSi film 14 is formed by forming an Ni film 15 on the SiGe film 12which has been selectively formed on the Si substrate 11 by epitaxialgrowth on the Si substrate 11, and then siliciding the Ni film 15. FIG.7 is a detailed view showing the vicinity of the Si substrate 11 in FIG.6. This will be described in detail below.

The SiGe film 12 with a thickness of about 60 nm is formed by theabove-described step on the p-type Si (1 0 0) substrate 11 having theinsulating isolation region pattern 13, i.e., the p-type SOI wafer 11.An oxide film 16 and source/drain region (N⁺ region) 17 containingsilicon are formed on the p-type SOI substrate 11. In addition, a gate18 containing Si and gate sidewalls 19 and 20 made of an insulatingmaterial are formed on the p-type SOI substrate 11.

As described above, the SiGe film 12 is formed on the region of thep-type SOI substrates 11 where no insulators represented by a TEOS film(insulating isolation region pattern) 13 are formed. More specifically,the SiGe film 12 is contiguous to the source/drain region (N⁺ region) 17formed on the uppermost portion of the Si substrate 11, and is elevatedon the surface of the source/drain region (N⁺ region) 17. That is, theSiGe film 12 forms a so-called elevated source/drain region structuretogether with the source/drain region 17.

The p-type SOI substrate 11 is cleaned by a diluted hydrofluoric acid(HF) immediately after the SiGe film 12 is epitaxially grown on thesource/drain region 17. Subsequently, the p-type SOI substrate 11 isintroduced into the chamber of the sputtering apparatus. In thischamber, an Ni film 15 is deposited to a thickness of about 30 nm bysputtering on the surface of the SiGe film 12 which has been formed bybeing elevated on the surface of the p-type SOI substrate 11.

Then, the p-type SOI substrate 11 with the Ni film 15 is introduced intothe chamber of a rapid thermal anneal system (RTA system). The p-typeSOI substrate 11 undergoes annealing. More specifically, the p-type SOIsubstrate 11 undergoes annealing by the same multi-step annealing as inthe first embodiment. In this embodiment, however, the p-type SOIsubstrate 11 is heated stepwise in the range of about 400° C. to about700° C. The Ni film 15 on the SiGe film 12 is silicided by theabove-described steps. NiSi films 14 are thus formed on the p-type SOIsubstrate 11. More specifically, above the p-type SOI substrate 11, theNiSi films 14 are selectively formed on the respective surfaces (uppersurfaces) of the gate 18 and the SiGe film 12 formed by being elevatedon the p-type SOI substrate 11. Consequently, a MOS transistor 21serving as a semiconductor element is formed.

Thereafter, a desired semiconductor device 22 shown in FIG. 7 isobtained through the predetermined steps. That is, the semiconductordevice 22 is obtained which includes the MOS transistor 21 in which theNiSi films 14 are formed on only the respective surfaces (uppersurfaces) of the gate 18 and the SiGe film 12 with the so-calledelevated source/drain structure.

According to experiments that have been conducted by the presentinventors, in the NiSi film 14 formed on the SiGe film 12 by themulti-step annealing of this embodiment, the annealing temperaturedependence on the sheet resistance of the NiSi film 14 represents atendency shown in a graph in FIG. 8. In particular, when the annealingtemperature is set at less than 700° C., the sheet resistance of theNiSi film 14 in this embodiment can be kept as very low as a maximum ofabout 2 Ω/□.

As described above, according to the second embodiment, the same effectsas in the first embodiment can be obtained. In addition, a filmincluding a composite structure of an NiSi film 14 and SiGe film 12,which has greatly improved electrical characteristics and a stablecomposition even at high temperatures in a semiconductor devicemanufacturing process, can be formed on the Si substrate 11. Morespecifically, a source/drain structure in the SOI-MOSFET transistor 21serving as a MOS transistor is formed by, e.g., adding an NiSi film 14with good electrical characteristics to the elevated source/drainstructure formed by forming the SiGe film 12 on the surface of thesource/drain region 17. As a result, the electrical characteristics ofthe SOI-MOSFET 21, and the semiconductor device 22 including theSOI-MOSFET 21 can be improved.

As described above, according to the nickel-silicon compound formingmethod in this embodiment, a nickel silicide 14 of good quality with alow resistance can be formed on not only Si 11 but also the compound 12containing silicon represented by SiGe. In addition, according to thesemiconductor device manufacturing method in this embodiment to whichthe nickel-silicon compound forming method in this embodiment isapplied, the semiconductor element 21 is formed by using a nickelsilicide 14 of good quality with a low resistance, so that theelectrical characteristics of the semiconductor element 21 can beimproved. The electrical characteristics of the semiconductor device 22including the semiconductor element 21 described above can be improved.The semiconductor device 22 in this embodiment manufactured by applyingthe nickel-silicon compound forming method in this embodiment thereforehas improved electrical characteristics.

Note that the nickel-silicon compound forming method, semiconductordevice manufacturing method, an d semiconductor device according to thepresent invention are not limited to the first and second embodimentsdescribed above. The present invention can be practiced by modifyingsome steps in the first and second embodiments into various settings orappropriately using a proper combination of various types of settingswithout departing from the spirit and scope of the present invention.

For example, the starting temperature of the multi-step annealing, andthe period of time, the period, and the number of steps which arerequired for the heat increasing step and temperature keeping step inthe multi-step annealing, or the period of time required for theheat-insulating step and cooling step thereafter are appropriately setin proper values, so that an NiSi film of desired quality can be formed.In addition, the substance underlying the NiSi film is not limited tothe Si substrate or SiGe film, and any substance containing Si may beused.

Also, the thickness of the formed NiSi film or the thickness of anunderlying film formed from only silicon or a compound containingsilicon can be appropriately set in a proper value in accordance withthe film formation condition or desired electrical characteristics ofthe semiconductor element or semiconductor device.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit and scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A nickel-silicon compound forming method comprising: forming nickelon at least one of only silicon and a compound containing silicon; andperforming stepwise-heating of the nickel together with said at leastone of only silicon and the compound containing silicon, wherein atemperature is raised and maintained alternately.
 2. A method accordingto claim 1, wherein the stepwise heating includes: after the nickel isheated from a temperature T₀ to a temperature of T₁ together with saidat least one of only silicon and the compound containing silicon;repeating a plurality of times a step of increasing, by a temperature ΔTover a period of time S₁, the temperature T₁ of the nickel and said atleast one of only silicon and the compound containing silicon, andkeeping a resultant temperature for a period of time S₂; and therebyheating the nickel from the temperature T₀ to a temperature T₂ by thetemperature ΔT stepwise together with said at least one of only siliconand the compound containing silicon.
 3. A method according to claim 2,wherein in the stepwise heating, the period of time S₁ is shorter thanthe period of time S₂.
 4. A method according to claim 2, wherein in thestepwise heating, the temperature ΔT is lower than a difference betweenthe temperature T₁ and temperature T₀.
 5. The method according to claim2, wherein the nickel is heated to the temperature T₂ stepwise togetherwith said at least one of only silicon and the compound containingsilicon, and the temperature T₂ is then kept for a period of timesubstantially equal to that required for the stepwise heating.
 6. Themethod according to claim 2, wherein the nickel is heated to thetemperature T₂ stepwise together with said at least one of only siliconand the compound containing silicon, the temperature T₂ is kept for aperiod of time substantially equal to that required for the stepwiseheating, and the nickel is then cooled to the temperature T₀.
 7. Themethod according to claim 2, wherein in the stepwise heating, thetemperature T₁ is not more than 350° C., and the temperature T₂ fallswithin a range between 450° C. (inclusive) and 900° C. (exclusive). 8.The method according to claim 2, wherein the compound containing siliconincludes silicon germanium.
 9. A method according to claim 1, whereinthe compound containing silicon includes silicon germanium.
 10. Themethod according to claim 1, wherein nickel mono silicide is formed onsaid at least one of only silicon and the compound containing silicon.11. The method according to claim 1, comprising more than one timeperiod of maintaining the temperature following a time period of raisingthe temperature, and each time period of maintaining the temperature isthe same.
 12. The method according to claim 1, comprising a time periodof maintaining the temperature following time periods of raising thetemperature, and each time period of raising the temperature is thesame.
 13. The method according to claim 1, comprising a time period ofmaintaining the temperature following two or more time periods ofraising the temperature, and each rise in temperature is the same.
 14. Asemiconductor device manufacturing method comprising: forming anickel-silicon compound on a semiconductor element comprising at leastone of only silicon and a compound containing silicon; wherein thenickel-silicon compound is formed on the semiconductor element by;forming nickel on said at least one of only silicon and the compoundcontaining silicon; and performing stepwise-heating of the nickeltogether with said at least one of only silicon and the compoundcontaining silicon, wherein a temperature is raised and maintainedalternately.
 15. The method according to claim 14, wherein the stepwiseheating includes: after the nickel is heated from a temperature T₀ to atemperature T₁ together with said at least one of only silicon and thecompound containing silicon; repeating a plurality of times a step ofincreasing, by a temperature ΔT over a period of time S₁, thetemperature T₁ of the nickel and said at least one of only silicon andthe compound containing silicon, and keeping a resultant temperature fora period of time S₂; and thereby heating the nickel from the temperatureT₀ to a temperature T₂ by the temperature ΔT stepwise together with saidat least one of only silicon and the compound containing silicon. 16.The method according to claim 15, wherein in the stepwise heating, theperiod of time S₁ is shorter than the period of time S₂.
 17. The methodaccording to claim 15, wherein in the stepwise heating, the temperatureΔT is lower than a difference between the temperature T₁ and temperatureT₀.
 18. The method according to claim 15, wherein the nickel is heatedto the temperature T₂ stepwise together with said at least one of onlysilicon and the compound containing silicon, and the temperature T₂ isthen kept for a period of time substantially equal to that required forthe stepwise heating.
 19. The method according to claim 15, wherein thenickel is heated to the temperature T₂ stepwise together with said atleast one of only silicon and the compound containing silicon, thetemperature T₂ is kept for a period of time substantially equal to thatrequired for the stepwise heating, and the nickel is then cooled to thetemperature T₀.
 20. The method according to claim 15, wherein in thestepwise heating, the temperature T₁ is not more than 350° C., and thetemperature T₂ falls within a range between 450° C. (inclusive) and 900°C. (exclusive).
 21. The method according to claim 15, wherein thecompound containing silicon includes silicon germanium.
 22. The methodaccording to claim 14, wherein the compound containing silicon includessilicon germanium.
 23. The method according to claim 14, wherein thesemiconductor clement includes a transistor, and the nickel-siliconcompound is formed at least one of a source, drain, and gate of thetransistor.
 24. The method according to claim 23, wherein nickel monosilicide is formed as the nickel-silicon compound.